Green Moon's jockey Brett Prebble has question marks over Atlantic Jewel at 2000 metres while the horse he fears most heading towards Saturday's Caulfield Stakes is in doubt for the race.

Prebble has taken plenty of positives out of reigning Melbourne Cup winner Green Moon's two spring starts and is looking forward to the import stepping to 2000m in Saturday's Group One weight-for-age race at Caulfield.

Awaiting him in the Caulfield Stakes will be outstanding mare Atlantic Jewel who was defeated for the first time in her 10 starts when It's A Dundeel got the better of her in the Underwood Stakes (1800m).

A rematch between the pair may not happen with trainer Murray Baker battling to get him ready after a recurrence of a foot abscess.

Green Moon was fifth to Atlantic Jewel in the Memsie Stakes (1400m) first-up and Prebble said he wasn't suited by the on-pace dominated Underwood Stakes when ninth, four lengths behind It's A Dundeel and Atlantic Jewel.

Green Moon won the Turnbull Stakes (2000m) third-up last spring and Prebble believes he is fit and ready to make his presence felt stepping up in distance.

"I think the horse is going fantastic," Prebble said.

"He just needs to get into a race where it's going to be run to suit.

"He's had two runs now, he's fit, and he should be running well."

The Mark Kavanagh-trained Atlantic Jewel won the Wakeful Stakes by a big margin over 2000m as a three-year-old against her own age and sex and the mare is favourite for the Cox Plate (2040m).

"Atlantic Jewel, I've really got big question marks on her at this level over 2000 metres," Prebble said.

"I think she's a miler. She was found out last time by a good colt. Maybe the softish ground didn't help, I'm not sure, but she was in the right place and he (It's A Dundeel) gunned her down.

"Is going to the 2000 metres a plus or a negative (for Atlantic Jewel)? For mine, I think it's a negative."

Prebble said he was "more scared" of a fit It's A Dundeel.